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  #1  
Old 10-11-2013, 06:00 AM
david.perl's Avatar
david.perl david.perl is offline
 
Join Date: Dec 2010
Location: Watford UK
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Default An expensive mistake - over-reamed taper pin hole for 7A nose gear.

I knew my build was going to well. Ive just finished the canopy with no issues and was working on drilling out the nose leg on my 7A for a taper pin.

I've gone too deep with the reamer (broke the first one and in my excitement to get the hole finished with the new reamer i didn't check the depth often enough. I had the first reamer marked with tape to warn me but in my haste didn't bother with the new reamer. Like others, reaming the hole was a pig and than it suddenly started cutting and i got carried away in my excitement at making chips.

Its about 1/8 inch too deep but looks like an expensive 1/8 inch. I got that horrible sickening feeling when you know you've screwed up big time.

Ive got a quote from a manufacturer of taper pins of $900 for one pin (ouch) and am awaiting a local machine shop to quote. The Cadmium plating alone has a minimum charge of $160 (UK prices). Im looking at Stainless Steel as an option.

Im wondering what other options are there? At this rate a new engine mount and nose gear will be cheaper. Can i get a new nose leg and weld the holes in the engine mount and re-ream the mount? Can i just enlarge the hole to take an AN6 bolt?

Any thoughts welcome and hopefully my mistake can help others.

Main thing is no one got hurt.

cheers

David
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  #2  
Old 10-11-2013, 06:23 AM
Randle Randle is offline
 
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Default Talk to the Russ

Get ahold of Russ McCutcheon, he is a member on here and I am pretty sure he manufactures the engine mount for Vans Aircraft. He would be the most knowledgeable person on here and can give you the best advice. Here is his contact info.
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  #3  
Old 10-11-2013, 07:38 AM
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Greg Arehart Greg Arehart is offline
 
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Location: Delta, CO/Atlin, BC
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Default

I would think you have multiple options, all but the last of which you have already mentioned, and listed here in order of probable cost: 1. weld the hole on the engine mount, buy a new gear leg, and start over (I don't think you can weld the gear leg without changing the stress characteristics of that steel, but am not entirely certain of that); 2. Enlarge for a close-tolerance AN bolt (would check with Vans to make certain you don't enlarge over a safe margin; 3. buy two new parts and start over; 4. get a larger/longer taper pin; 5. convert to a TW (had to add that one).

Best of luck,
Greg

p.s. I've done #2 for my gear legs when the original bolt holes got a bit wallowed out.
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  #4  
Old 10-11-2013, 07:51 AM
868RM 868RM is offline
 
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Location: lena, il.
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Default taper

David, Are you using a standard 1/4 inch per 12 inch taper? If you are , 1/8 in. to deep is less than .003 in. dia. McMaster-Carr has stainless in lengths like 6 or 7 in. long. You could get one (1) size bigger x long and use the section you need. A stainless #7 x 6 in. is $9.76 in the U.S. Big end is .409, small end is .284. Has a breaking strength of 54,000 psi. & rockwell B85 hardness. Hope this helps Ron
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  #5  
Old 10-11-2013, 07:55 AM
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scard scard is offline
 
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You'll be fine. Stop, think, and do not spend $900! I don't know what hardware you're using, but taper pins come in a vast array of sizes. Any reasonable machine shop should be able to make one up, or better yet, modify one that is too big. The material here is quite important. Consider that carefully.
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  #6  
Old 10-11-2013, 07:58 AM
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david.perl david.perl is offline
 
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Thanks Ron, Ive used the number 3 B&S taper reamer as recommended. This has a taper of 0.500"/ft

The ACS supplied pins have tensile strength of 125,000 PSI. does this mater if its less? So your suggesting i get a longer length of tapered SS and cut threads on the end? Sounds like a good idea.

Also McMaster-Carr wont mail to the UK.
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  #7  
Old 10-11-2013, 10:13 AM
terrykohler terrykohler is offline
 
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Default Don't Know if Stainless is a Good Idea

I'd definitely check with Vans on that one. Arbitrarily swapping out for another material with less than half the tensile (and shear) on a part that helps hold up the front end of the airplane is something I'd want to get an approval on.
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  #8  
Old 10-11-2013, 10:19 AM
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Russ McCutcheon Russ McCutcheon is offline
 
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Quote:
Originally Posted by Randle View Post
Get ahold of Russ McCutcheon, he is a member on here and I am pretty sure he manufactures the engine mount for Vans Aircraft. He would be the most knowledgeable person on here and can give you the best advice. Here is his contact info.
__________________
www.mccutcheonmetalfabricationaviation.com
russmccutcheon@gmail.com
We build many of your RV weldments.
I did not have the answer for him, I suggested he ask Van's.
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  #9  
Old 10-11-2013, 11:36 AM
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david.perl david.perl is offline
 
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Location: Watford UK
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Heres the response from Vans:

You can weld a patch on the engine mount and drill a new hole but that could change the shape of the socket out of round and require you to have it honed again. The other alternative is if the hole was drilled in the center of the nob on top of the gear leg you can go up to an AN6 bolt. The only problem with going to the AN6 is if you have a problem again you will have to weld up or replace the mount and gear leg (gear leg can not be welded).


Im apprehensive about drilling the hole out to AN6 size in case i mess it up.Any suggestions on how to minimise errors in drilling a tapered hole to a parallel one? Ill also get a quote from a smaller local machine shop more setup to smaller runs
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Old 10-11-2013, 01:15 PM
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rzbill rzbill is offline
 
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Default

I want to make sure I understand what you said in the original post.

I read that the hole is too large by an amount that allows the pin to penetrate 1/8" further than desired.

I put taper pins in also but I don't have a picture in my build log and I'm not at the hangar.
Please look at the link below and let us know if that image is close.

Nose strut taper pin install (from matronics)

If it is, then I suspect your unthreaded end of the pin remains functional by a good margin even though it is further in by 1/8". My path might be to simply make a different washer/spacer on the threaded end and call it a day.

Obviously if the unthreaded end of the pin is radially inward of the gearmount outer surface, then you have the problem discussed in the thread. If not, I'd build on.

Can you insert the pin into the gear and mount and post a pic?
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Last edited by rzbill : 10-11-2013 at 01:17 PM.
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